A North Clarendon exterminator has had his license suspended and state officials are trying to contact his clients in the Rutland area.

The state Agency of Agriculture, Food and Markets announced this week it had suspended the pesticide applicator license of Cary Buck of AAA Accredited Pest Control for allegedly using a chemical not approved for indoor use.

State officials said Buck used an insecticide called chlorpyrifos to spray for bedbugs despite the fact that the Environmental Protection Agency banned its indoor use in 2001.

“We received a call from folks who were very concerned that their house smelled awful after a bedbug treatment was made,” said Gary Giguere, pesticide section chief for the Agency of Agriculture.

Giguere said the agency did testing and found the banned chemical in such high amounts that the family was “very fortunate” they had not reoccupied the house following the spraying as they likely would have suffered serious health effects.

The agency declined to identify the home where the spraying took place.

Working with the state Department of Health and the EPA, the Agency of Agriculture is sending letters out to Buck’s other recent customers, and anyone contacted can have their home tested free of charge. They said company records indicate as many as 50 homes could be affected, but they did not know how many times the chemical was used in those homes.

Contacted about the investigation Thursday, Buck denied using chlorpyrifos.

“There’s been five other exterminators at that place before I was there in the last five years,” he said. “I am the only exterminator in this state, I believe, who gives a guarantee. Other exterminators don’t like me because of that — they say I’m going to ruin their business. ... I did not do it. I am not guilty of it. That’s all.”

Dr. Harry Chen, Vermont’s health commissioner, said containers of chlorpyrifos were found in Buck’s basement and that the state had tested 11 locations Buck had sprayed in the last 1½ years, with five coming back positive, two coming back negative and four results still pending.

“Our advice to some of them was they should relocate within 48 hours, some that they did not need to relocate and some they should relocate within a week,” Chen said.

Chen said chlorpyrifos is a neurotoxin whose effects can include memory loss and numbness, with particular danger to children and pregnant women. He said the state had not yet located anyone made sick by the spraying.

“The nice thing about this chemical is, once you leave, the effects go away,” he said. “It doesn’t cause cancer. Its effects are acute.”

Chen said cleaning up from such a spraying is a challenge his department and the EPA are discussing. He said homeowners are advised against cleaning up on their own and that soft woods and porous materials may not be able to be cleaned.

Giguere said he was aware of similar cases in recent years in Ohio and Massachusetts, the latter resulting in criminal charges, but that this was a first for Vermont.

Giguere said chemicals alone have a poor record of controlling bedbugs, but that exterminators have had success with integrated pest management techniques including traps, heat treatment and spraying in cracks and crevices.

“You should be spraying nothing yourself, that would be our first bit of advice,” he said. “What we would say is combining chemicals and nonchemical treatments in a unified approach is what makes the most sense.”